Answer:63 solution custom sub form

apps/forms/63-custom-forms/src/app/address-form.component.ts

@@ -0,0 +1,81 @@
+import { ChangeDetectionStrategy, Component, input } from '@angular/core';
+import {
+  FieldState,
+  FieldTree,
+  FormField,
+  required,
+  SchemaPathTree,
+} from '@angular/forms/signals';
+
+interface AddressGroup {
+  street: string;
+  zipcode: string;
+  city: string;
+}
+
+export const defaultAddress: AddressGroup = {
+  street: '',
+  zipcode: '',
+  city: '',
+};
+
+export const addressSchema = (item: SchemaPathTree<AddressGroup>) => {
+  required(item.street);
+  required(item.zipcode);
+  required(item.city);
+};
+
+@Component({
+  selector: 'app-address-form',
+  imports: [FormField],
+  changeDetection: ChangeDetectionStrategy.OnPush,
+  template: `
+    <div class="grid gap-4 sm:grid-cols-2" data-testid="shipping-fields">
+      <label
+        class="flex flex-col gap-1 text-sm font-medium text-slate-700 sm:col-span-2">
+        Street
+        <input class="input" type="text" [formField]="form().street" />
+        <span class="hint">
+          @if (showError(form().street())) {
+            This field is required
+          }
+        </span>
+      </label>
+      <label class="flex flex-col gap-1 text-sm font-medium text-slate-700">
+        ZIP code
+        <input class="input" type="text" [formField]="form().zipcode" />
+        <span class="hint">
+          @if (showError(form().zipcode())) {
+            This field is required
+          }
+        </span>
+      </label>
+      <label class="flex flex-col gap-1 text-sm font-medium text-slate-700">
+        City
+        <input class="input" type="text" [formField]="form().city" />
+        <span class="hint">
+          @if (showError(form().city())) {
+            This field is required
+          }
+        </span>
+      </label>
+    </div>
+  `,
+  styles: [
+    `
+      .input {
+        @apply w-full rounded-lg border border-slate-300 bg-white px-3 py-2 text-sm shadow-sm outline-none transition focus:border-indigo-500 focus:ring-2 focus:ring-indigo-200;
+      }
+      .hint {
+        @apply text-xs text-rose-600;
+      }
+    `,
+  ],
+})
+export class AddressFormComponent {
+  form = input.required<FieldTree<AddressGroup>>();
+
+  showError<T>(field: FieldState<T>): boolean {
+    return field.invalid() && (field.touched() || field.dirty());
+  }
+}